1. Field of the Invention
The present invention relates to structures of turbine scroll and blades. The turbine scroll forms the gas flow path for radial turbines used in turbochargers for internal combustion engines (exhaust gas turbocharger), small turbines, expansion turbines, etc., wherein the operating gas flows onto the turbine blades on the turbine rotor from the vortex-shaped scroll in the radial direction to impart rotational drive to said turbine rotor. The turbine blades are fixed on a rotor shaft for the compressor.
2. Description of the Related Art
Radial turbines are widely used in the relatively compact turbochargers (exhaust gas turbochargers) used in automobile engines and the like. The operating gas for the turbine flows in the radial direction from the vortex-shaped scroll formed inside the turbine casing to the turbine blades, causing the rotation of said turbine rotor, before flowing in the axial direction.
FIG. 11 shows an example of a turbocharger using a radial turbine. In the Figure, 1 represents the turbine casing, 4 the vortex-shaped scroll formed inside turbine casing 1, 5 the gas outflow path formed inside turbine casing 1, 6 the compressor casing, and 9 the bearing housing that links the turbine casing 1 and compressor casing 6.
Turbine rotor 10 has a plurality of turbine blades 3, which are evenly spaced and affixed to its outer circumference. 7 is the compressor, 8 the diffuser mounted at the air outlet of said compressor 7, and 12 is the rotor shaft that links said turbine rotor 10 and compressor 7. 11 is a pair of bearings mounted in the foregoing housing 9, which support the foregoing rotor shaft 12. 20 is the axis of rotation of the foregoing turbine rotor 10, compressor 7 and rotor shaft 12.
In turbochargers equipped with such radial turbines, exhaust gases from the internal combustion engine (not shown) enter the foregoing scroll 4, where they flow along the swirl of said scroll 4, which causes them to rotate as they flow in from the opening at the outside circumference of the turbine blades 3 toward said turbine blades 3 in the radial direction toward the center of turbine rotor 10. After performing the expansion work upon said turbine rotor 10, the gases flow in the axial direction outside of the device through gas outlet 5.
FIG. 12 is a structural diagram showing the foregoing scroll 4 and surrounding area in a radial turbine. In the figure, 4 is the scroll, 41 the outer circumferential wall of said scroll 4, 43 the inner circumferential wall, and 42 the side walls. Also, 3 represents the turbine blades, 36 the shroud side and 34 is the hub side for said turbine blades 3.
The width xcex94R0 in the radial direction of scroll 4 is formed to be of approximately the same dimensions as the width B0 in the direction of the axis of rotation (scroll width ratio xcex94R0/B0=1).
FIG. 13(A), FIG. 13(B) show the area around a tongue formed in inner circumference of the gas inlet to the radial turbine; FIG. 13(A) is a front view from a right angle to the axis of rotation, and FIG. 13(B) is a view in the direction of the arrows on line Bxe2x80x94B of FIG. 13(A).
In the FIGS. 13(A), 13(B), 4 is the scroll, 44 is the edge surface of the opening to said scroll 4, 45 the tongue formed on the inside circumference of the gas inlet, 45a is the tongue edge, the downstream edge of said tongue 45, and 046 represents the tongue""s downstream side walls, which are located directly downstream of tongue edge 45a of the foregoing scroll 4.
The width between the walls of said tongue""s downstream side walls 046 is either the same as the width of the foregoing tongue edge 45a, or a width that has been smoothly constricted from tongue edge 45a to follow the shape of the scroll 4.
In the above described types of radial turbines, the gases inflowing into the vortex of the foregoing scroll are rotating as they flow into turbine blades 3, and the velocity distribution of the inflowing gas varies in the height direction (Z direction) of turbine blades 3.
To wit, due to the three dimensional boundary layer having a 15 to 20% height B3 range at the foregoing input edge surface formed in the vicinity of inlet edge surface 31 (see FIG. 12) for the foregoing turbine blades 3, the foregoing gas inflow velocity C, as shown in FIG. 14, has a circumferential direction component having a circumferential velocity Cxcex8, which is greater at the center of the foregoing inlet edge surface 31, and which is lower at the square area on both ends of the blades 3, i.e. the shroud side 36 and the hub side 34. Also, as shown in FIG. 11, the radial direction component, which is the radial direction velocity CR, has a distribution in the height direction, which is lower in the center of the foregoing inlet edge surface 31 and higher at both edges, i.e. the shroud side 36 and the hub side 34.
Then when distribution in the flow in the height direction at the inlet to the foregoing turbine blades 3 exists, in other words, when there is distortion in the flow, the flow loss at said turbine rotors increases, and this lowers the turbine""s efficiency. To wit, the optimum relative angle of gas inflow xcex21, along with relative angle of gas inflow xcex22 between the walls of inlet edge walls 31, i.e. between the foregoing hub side 34 and shroud side 36, in the center of the inlet for turbine blades 3 increases, so that near the foregoing hub side 34 and shroud side 36, a difference develops in the relative angle of gas inflow xcex2. In other words, as the gas impact angle (incidence angle) increases, the impact angle (incidence angle) also increases on the back side of turbine blades 3 from the gas (back pressure), which not only causes impact loss, but it increases the impact angle (incidence angle) at the foregoing hub side 34 and shroud side 36, which adds to the secondary flow loss between the turbine blades to thereby lower the turbine""s efficiency.
On the other hand, in the foregoing scroll 4, which forms the inlet flow path to the turbine blades 3, the shape of the scroll 4 causes a three dimensional boundary layer to be produced. As shown in FIG. 15(B), the radial direction velocity CR in the height direction of turbine blades 3, shows a velocity distribution which is lower at the center of the foregoing inlet edge surface 31, and higher at the square areas on the two ends of the blades, in other words, on the shroud side 36 and the hub side 34.
However, as shown for the conventional scroll 4 in FIGS. 12 and 13:
(1) the cross-sectional shape of the flow path of scroll 4 is approximately square, with the width dimension in the radial direction xcex94R0 being the same as the width in the direction of the axis of rotation B0 (scroll width ratio xcex94R0/B0=1).
(2) In the area on both sides of scroll 4 which connect to around both edges of turbine blades 3, to wit the shroud side 36 and the hub side 34, the side walls have a smooth surface.
(3) The width Bo in the direction of the axis of rotation of the scroll 4 flow is formed to be either constant, or diminished slightly toward the inside circumferential side.
These result in the following types of problems:
Due to that structure, the above described three dimensional boundary layer is apt to form at the gas inlet to the foregoing turbine blades 3.
Further, in the area of the foregoing tongue 45, the difference in pressure above and below tongue 45 due to its thickness causes the generation of wake 50, as shown in FIG. 13(A). Then, as shown in FIG. 13(A) for the conventional technology, since width between the walls downstream of the tongue 046, being either the same as the width of the tongue edges 45a or gradually reduced from said tongue edge 45a, following the shape of scroll 4, generates no action that would reduce the foregoing wake 50. Accordingly, as shown in FIG. 15(A), this causes variation and distortion the radial direction velocity CR in the circumferential direction.
Thus, in the prior art, the shape of scroll 4 as stated above in (1), (2) and (3) causes a three dimensional boundary layer to be generated, which distorts the gas flow in the height direction of turbine blades 3 as the gas flows into the turbine blades, and this increases the flow loss to turbine blades 3, and thereby lowers the turbine efficiency.
Further, due to the structure of the side walls 046 downstream of the foregoing tongue edge 45a in the prior art, the thickness T of tongue 45 does not act to reduce the wake 50, and even further causes variation and distortion in the boundary layer of the radial direction velocity CR in the circumferential direction. This increases the scroll flow loss, and thereby lowers turbine efficiency.
On the other hand, since the shape of the aforementioned turbine blades 3 is such that the outside diameter of the inlet edge surface 31 maintains the same height across the shroud side 36, the center area, and hub side 34 as shown in the B portion shown in FIG. 16(A), the blades"" circumferential velocity U2=U1. Because of this, the relative angle of gas inflow xcex2 in the height direction of the blades 3 differs. If, as shown in the E portion shown in FIG. 16(A), the relative angle of gas inflow xcex21 is optimized in the center area, then, as shown in FIG. D portion in FIG. 16(A), the relative angle of gas inflow xcex22 near the side walls, i.e. hub side 34 and shroud side 36, is greater than the relative angle of gas inflow xcex21 at the center due to the flow distortion caused by the foregoing scroll 4. In the figures, W1, W2 are the relative gas inflow velocities, and C1, C2 are the absolute gas inflow velocities.
Due to this situation in the prior art, on the foregoing hub 34 and shroud 36 sides, the gas flow on the back side (negative pressure side) of the foregoing blades 3 came in at an impact angle (incidence angle) and not only generated an impact loss at the inlet to the turbine blades, but also increased the secondary flow loss inside turbine blades 3 due to the increase of the impact angle (incidence angle) on the forgoing hub 34 and shroud 36 sides, which facilitated diminished turbine efficiency.
The present invention was developed after reflection upon the problems associated with the prior art. The improvements are made in the turbine scroll and the turbine blades. The first object of this invention is to provide a scroll structure for radial turbines that inhibits the formation of a three dimensional boundary layer caused by the shape of the scroll at the inlet to the turbine blades, that reduces the flow loss to said turbine blades by preventing distortions from forming in the gas flow in the height direction of said turbine blades, and that additionally inhibits the scroll flow loss by reducing the formation of distortion in the radial direction velocity in the scroll flow path as means to improve turbine efficiency.
The second object of this invention is to provide turbine blades which can improve the efficiency of the turbine by making the relative angle of gas inflow at the inlet to the turbine blades uniform in the height direction of the blades and inhibiting the gas impact loss due to variations in the foregoing relative angle of gas inflow and the generation of secondary flows in the area inside the turbine blades.
To achieve the first objects mentioned above improving the shape of the scroll, a preferred embodiment of this invention provides radial turbines in which the operating gas flows through a vortex-shaped scroll formed inside the turbine casing to the blades of the turbine rotor positioned inside that scroll, flowing into said blades in a radial direction to rotate said turbine rotor before flowing out, in the axial direction, wherein the scroll structure for the radial turbines is characterized by the foregoing scroll having a scroll width ratio between the width in the radial direction (xcex94R) and the width in the direction of the rotation (B) ranging from xcex94R/B=0.3 to 0.7.
As shown in FIG. 1, by means of this invention providing that the scroll width ratio between the width of the scroll in the radial direction (xcex94R) and the width in the direction of the axis of rotation (B) being xcex94R/B=0.3 to 0.7, creates a situation where the total friction loss caused by the scrolls side walls and the inside and outside circumferential walls is approximately equivalent to that in the prior art where the width ratio was xcex94R/B=1, but because the scroll shape has been flattened by lengthening width in the axial direction of rotation (B) to be approximately twice the width in the radial direction (xcex94R), at the edge area of the blades (to wit, on the shroud side and the hub side) on the scroll side walls, the radial direction velocity (CR) has been reduced over what it was in the prior art wherein the aforementioned scroll width ratio xcex94R/B was approximately 1. This reduces the secondary flow loss inside the scroll.
It further serves to inhibit the development of a three dimensional boundary layer, which, as shown in FIG. 2, reduces the flow loss, especially the mixture loss to the turbine blades, by maintaining the distortion of the gas flow in the direction of the height of the turbine blades as it flows into the blades to thereby improve the efficiency of the turbine.
Another preferred embodiment of this invention is characterized by the foregoing scroll being structured in a manner such that the width in axial direction of rotation (B) expands at a fixed rate from the outside circumference in the radial direction toward the inside circumference.
Another preferred embodiment of this invention, is preferably, is characterized by the foregoing scroll""s width in the direction of the axis of rotation (B) being formed so that the width in the axial direction of the inside circumferential edge (B2) being 1.2 to 1.5 times the width of the outside circumferential edge (B1).
According to this embodiment, the structure of the scroll is such that its width in the direction of the axis of rotation (B) is gradually expanded from outer circumferential side in the radial direction to the inner circumferential side, which, corresponding to the square areas on both ends of the blades (that is, on the shroud side and hub side), along both side walls of the scroll area, the velocity in the radial direction (CR) is gradually reduced as the gas approaches the turbine blades, which causes a more uniform distribution of the velocity in the radial direction (CR), in comparison to the reduction achieved in the prior art by using a constant scroll width.
This structure inhibits the development of a three dimensional boundary layer, and the turbine efficiency is improved by maintaining the turbulence in the gas in the height direction of the blades as it flows onto said blades to thereby reduce the flow loss and increase turbine efficiency.
Yet another preferred embodiment of this invention is characterized by forming a corrugated surface on the side walls of the foregoing scroll. This invention, by means of forming a corrugated surface on the side walls of the scroll, compared to that of the smooth surface in the prior art , causes a velocity reduction of the radial direction velocity (CR) due to the corrugated surface on both side walls of the scroll, in the areas that correspond to the square areas at both ends of the turbine blades (i.e. on the shroud side and hub side), which in turn causes the radial direction velocity (CR) distribution to become more uniform in the direction of the axis of rotation of said scroll.
This inhibits the development of a three dimensional boundary layer, and the gas flow in the height direction of the turbine blades remains distorted as it flows onto said blades to thereby reduce the flow loss and increase turbine efficiency.
Yet another preferred embodiment of this invention is characterized by forming the foregoing scroll in a manner such that, in a turbine scroll used in a radial turbine in which the operating gas flows through a vortex-shaped scroll formed inside the turbine casing to the blades of the turbine rotor positioned inside said turbine scroll, flowing into said blades in the radial direction to rotate the turbine rotor before flowing out, in the axial direction, it is characterized by the configuration wherein the sectional area of the tongue""s downstream formed at the inner circumference of the gas inlet is smaller than the sectional area of the tongue edge by narrowing in the width direction in an amount corresponding to the thickness (T) dimension of the tongue.
Preferably, the width of the tongue""s downstream side walls is formed partially narrower in an amount equal to the thickness (T) of said tongue than the width of the tongue edge.
According to this embodiment, by forming the scroll to make the sectional area of the flow path at the downstream right after the tongue smaller than the sectional area of the flow path at the tongue""s edge (especially, by making the width dimension between the walls at the downstream right after the tongue smaller by an amount corresponding to the thickness (T) of the tongue than the walls at the tongue edge, it is possible to reduce the wake generated by the tongue and to reduce the turbulence at the outlet of the scroll.
Further, reducing the width direction of the flow path at the downstream right after the tongue by an amount corresponding to the thickness (T) of the tongue, inhibits the development of a three dimensional boundary layer, and as was the case with the preferred embodiments mentioned above, the flow loss caused by the gas flow which remains distorted in the height direction of the turbine blades as it flows onto said blades can be reduced, and the turbine efficiency can be thereby increased.
To achieve the second objects mentioned above improving the shape of the blades, a preferred embodiment of the invention is related to a structure of turbine blades used in a radial turbine in which the operating gas flows through a vortex-shaped scroll formed inside the turbine casing to the turbine blades of the turbine rotor positioned inside said turbine scroll, flowing into said blades in the radial direction to rotate the turbine rotor before flowing out, in the axial direction. It is characterized by the configuration in which the turbine blades have cut-away areas at the blade corners by a prescribed amount, which are provided on the inlet edge at the shroud side and hub side where the operating gas flows.
The foregoing cut-away area can be a curve shaped cut-away which has a rounded sectional shape, or the foregoing cut-away area can have a linear sectional shape.
According to this configuration, the cut-away areas have been established on the shroud side and hub side of the inlet edge surface of the turbine blades, which makes the diameter of both ends of the foregoing inlet edge surface to be smaller than the diameter in the center. Accordingly, the amount that is cut away to form the foregoing cut-away areas can be varied to adjust to the gas flow distribution at the inlet to the turbine blades at the two ends of the inlet edge surface, i.e. relieved toward the inside circumference at the shroud side and the hub side, as a means to adjust to, the optimal angle in the height direction of the turbine blades for the relative inflow angle (xcex2) of the gas into the turbine blades.
Thus, according to the present embodiment, the gas impact angle (incidence angle) at the inlet to the turbine blades can be kept constant in the height direction of the blades, which avoids the issues in the conventional technology where there was impact loss and development of secondary flows inside the turbine blades due to the non-uniform relative gas inflow angles; such losses decreased the efficiency of turbines.
In addition, as described above, a three dimensional boundary layer forms with a width of about 10% to 20% the height of said inlet edge near the inlet edge surface of the turbine blades, and this three dimensional boundary layer causes the non-uniformity in the relative inflow angles in the height direction at the inlet to the turbine blades. However, as described above, by cutting away the foregoing inlet edge surface to at least match the width over which the three dimensional boundary layer is generated, that is, making the length in the radial direction of the cut-away area 10% to 20% of the height of the foregoing inlet edge surface, it is possible to eliminate the non-uniformity in the relative gas inflow angles between the center and the ends (shroud side and hub side) of the turbine blade inlet, to keep the gas incidence angle constant in the height direction of the inlet of the turbine blades.